R-T-B permanent magnet
阅读说明：本技术 R-t-b系永久磁铁 (R-T-B permanent magnet ) 是由 坪仓多惠子 增田健 于 2020-03-20 设计创作，主要内容包括：本发明提供一种即使在Co的含量少的情况下磁特性和耐腐蚀性也优异的R-T-B系永久磁铁。一种R-T-B系永久磁铁,其中,R为含有选自Nd和Pr中的1种以上,以及,选自Dy和Tb中的1种以上的稀土元素；T为Fe和Co；B为硼。R-T-B系永久磁铁还含有Zr。设R-T-B系永久磁铁整体为100质量％,则Nd、Pr、Dy和Tb的合计含量为30.00质量％～32.20质量％；Co的含量为0.30质量％～1.30质量％；Zr的含量为0.21质量％～0.85质量％；B的含量为0.90质量％～1.02质量％。(The invention provides an R-T-B permanent magnet having excellent magnetic properties and corrosion resistance even when the content of Co is small. An R-T-B permanent magnet, wherein R is a rare earth element containing 1 or more kinds selected from Nd and Pr and 1 or more kinds selected from Dy and Tb; t is Fe and Co; b is boron. The R-T-B permanent magnet further contains Zr. The total content of Nd, Pr, Dy and Tb is 30.00-32.20 mass% based on 100 mass% of the entire R-T-B permanent magnet; the content of Co is 0.30-1.30 wt%; the Zr content is 0.21-0.85 mass%; the content of B is 0.90-1.02 mass%.)
1. An R-T-B permanent magnet characterized in that,
r is rare earth element containing more than 1 selected from Nd and Pr, and more than 1 selected from Dy and Tb;
t is Fe and Co;
b is the component B of boron,
the R-T-B permanent magnet further contains Zr,
assuming that the total of the R-T-B permanent magnets is 100 mass%, then
The total content of Nd, Pr, Dy and Tb is 30.00-32.20 wt%;
the content of Co is 0.30-1.30 wt%;
the Zr content is 0.21-0.85 mass%;
the content of B is 0.90-1.02 mass%.
2. The R-T-B permanent magnet according to claim 1,
the R-T-B permanent magnet further contains Cu,
the Cu content is 0.10 to 0.55 mass%.
3. The R-T-B permanent magnet according to claim 1 or 2,
the R-T-B permanent magnet further contains Mn,
the Mn content is 0.02 to 0.10 mass%.
4. The R-T-B permanent magnet according to claim 1 or 2,
the R-T-B permanent magnet further contains Al,
the content of Al is 0.07-0.35 mass%.
5. The R-T-B permanent magnet according to claim 1 or 2,
the R-T-B permanent magnet further contains Ga,
the content of Ga is 0.02 to 0.15 mass%.
6. The R-T-B permanent magnet according to claim 1 or 2,
the content of the heavy rare earth element is 2.0 mass% or less.
7. The R-T-B permanent magnet according to claim 1 or 2,
there is a concentration gradient of the heavy rare earth element decreasing from the magnet surface toward the inside.
Technical Field
The present invention relates to an R-T-B permanent magnet.
Background
Patent document 2 discloses an R-T-B permanent magnet having high residual magnetic flux density and high coercive force.
Disclosure of Invention
Technical problem to be solved by the invention
An object of the present invention is to provide an R-T-B-based permanent magnet having excellent magnetic properties (residual magnetic flux density Br, coercive force HcJ, squareness ratio Hk/HcJ) and corrosion resistance even when the content of Co is small.
Means for solving the problems
In order to achieve the above object, the R-T-B permanent magnet of the present invention is characterized in that,
r is rare earth element containing more than 1 selected from Nd and Pr, and more than 1 selected from Dy and Tb; t is Fe and Co; b is the component B of boron,
the R-T-B permanent magnet further contains Zr,
assuming that the total of the R-T-B permanent magnets is 100 mass%, then
The total content of Nd, Pr, Dy and Tb is 30.00-32.20 wt%;
the content of Co is 0.30-1.30 wt%;
the Zr content is 0.21-0.85 mass%;
the content of B is 0.90-1.02 mass%.
The R-T-B permanent magnet of the present invention has a composition within the above range, and thus has excellent magnetic properties and corrosion resistance even when the content of Co is small.
The R-T-B permanent magnet may further contain Cu,
the content of Cu may be 0.10 to 0.55 mass%.
The R-T-B permanent magnet may further contain Mn,
the content of Mn may be 0.02 to 0.10 mass%.
The R-T-B permanent magnet may further contain Al,
the content of Al may be 0.07 to 0.35 mass%.
The R-T-B permanent magnet may further contain Ga,
the Ga content may be 0.02 to 0.15 mass%.
The content of the heavy rare earth element may be 2.0 mass% or less.
There may be a concentration gradient of the heavy rare earth element decreasing from the magnet surface toward the inside.
Drawings
Fig. 1 is a schematic view of an R-T-B permanent magnet according to the present embodiment.
Description of the symbols
1 … … R-T-B series permanent magnet
Detailed Description
Hereinafter, the present invention will be explained based on embodiments shown in the drawings.
< R-T-B based permanent magnet >
The R-T-B permanent magnet according to the present embodiment comprises a magnet composed of a magnet having R2T14And main phase grains composed of crystal grains having a B-type crystal structure. Further, there are grain boundaries formed by adjacent 2 or more main phase particles.
The shape of the R-T-B permanent magnet according to the present embodiment is not particularly limited.
The R-T-B permanent magnet according to the present embodiment can improve the remanence Br, the coercive force HcJ, the squareness ratio Hk/HcJ, and the corrosion resistance by containing a plurality of specific elements in specific ranges.
The R-T-B permanent magnet according to the present embodiment may have a concentration distribution in which the concentration of the heavy rare earth element decreases from the outside toward the inside of the R-T-B
Specifically, as shown in fig. 1, the rectangular parallelepiped R-T-B-based
Generally, rare earth elements can be classified into light rare earth elements and heavy rare earth elements. In the R-T-B permanent magnet according to the present embodiment, the light rare earth elements are Sc, Y, La, Ce, Pr, Nd, Sm, and Eu, and the heavy rare earth elements are Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
The method for forming the concentration distribution of the heavy rare earth element in the R-T-B permanent magnet according to the present embodiment is not particularly limited. For example, the concentration distribution of the heavy rare earth element can be formed in the R-T-B permanent magnet by grain boundary diffusion of the heavy rare earth element described later.
The main phase particles of the R-T-B permanent magnet according to the present embodiment may be core-shell particles each composed of a core and a shell covering the core. At least the shell may contain a heavy rare earth element, Dy or Tb, or Tb.
By making the heavy rare earth element exist in the shell, the magnetic properties of the R-T-B permanent magnet can be effectively improved.
In the present embodiment, a portion in which the ratio of the heavy rare earth element (e.g., Dy, Tb) to the light rare earth element (e.g., Nd, Pr) (heavy rare earth element/light rare earth element (molar ratio)) is 2 times or more the ratio in the central portion (core) of the main phase particle is defined as the shell.
The thickness of the shell is not particularly limited, but may be 500nm or less on average. The particle size of the main phase particles is not particularly limited, but may be 1.0 μm or more and 6.5 μm or less on average.
The method of forming the main phase particles as the core-shell particles is not particularly limited. For example, there is a method of grain boundary diffusion described later. The heavy rare earth element is subjected to grain boundary diffusion and is substituted with the rare earth element R on the surface of the main phase particle, thereby forming a shell having a high proportion of the heavy rare earth element and forming the core-shell particle.
R is a rare earth element containing at least 1 or more kinds selected from Nd and Pr, and 1 or more kinds selected from Dy and Tb. R preferably contains at least Nd and Tb.
T is Fe and Co.
B is boron. In addition, a part of boron contained in the B site of the R-T-B permanent magnet may be replaced with carbon (C).
The total content (TRE) of Nd, Pr, Dy, and Tb in the R-T-B permanent magnet according to the present embodiment is 30.00 mass% or more and 32.20 mass% or less, based on 100 mass% of the total mass of the R-T-B permanent magnet. When TRE is too low, HcJ decreases. When TRE is excessive, Br decreases.
The total content of Nd and Pr in the R-T-B permanent magnet according to the present embodiment is not particularly limited, and may be 29.27 mass% or more and 31.27 mass% or less, where the total mass of the R-T-B permanent magnet is 100 mass%.
The R-T-B permanent magnet of the present embodiment may contain at least Nd and Pr as R. The content of Pr may be 0.0 mass% or more and 10.0 mass% or less. Further, it may be 0.0 mass% or more and 7.6 mass% or less. When the content of Pr is 10.0 mass% or less, the temperature change rate of HcJ becomes small. Particularly, the content of Pr is preferably 0.0 to 7.6% by mass from the viewpoint of increasing HcJ at high temperature.
The content of Pr in the R-T-B permanent magnet according to the present embodiment may be 5.8 mass% or more, or less than 5.8 mass%. When the content of Pr is 5.8 mass% or more, HcJ is increased. When the content of Pr is less than 5.8 mass%, the rate of change in the temperature of HcJ becomes small.
When the content of Pr is 5.8 mass% or more, the content of Pr may be 5.8 mass% or more and 7.6 mass% or less. Pr/(Nd + Pr) may be 0.19 or more and 0.25 or less in terms of mass ratio. When the content of Pr and/or Pr/(Nd + Pr) is within the above range, HcJ is increased.
May intentionally contain no Pr. By intentionally not containing Pr, the rate of change in HcJ with temperature is particularly excellent, and HcJ at high temperatures becomes high. When Pr is intentionally not contained, Pr may be contained in an amount of less than 0.2 mass% or 0.1 mass% or less as an impurity.
In the R-T-B permanent magnet of the present embodiment, the total mass of all the R-T-B permanent magnets is defined as 100 mass%, and the total mass of heavy rare earth elements (for example, 1 or more selected from Dy and Tb) may be 2.0 mass% or less. It may actually contain only Tb as a heavy rare earth element. When the content of the heavy rare earth element is 2.0 mass% or less in total, Br is easily made good. Further, by reducing the content of expensive heavy rare earth elements, it becomes easy to manufacture R-T-B permanent magnets at low cost.
The content of Co may be 0.30 to 1.3 mass%, or 0.30 to 0.43 mass%, based on 100 mass% of the total mass of the R-T-B permanent magnet. In the present embodiment, an R-T-B permanent magnet having high corrosion resistance can be obtained even if it contains a small amount of expensive Co. As a result, it becomes easy to manufacture R-T-B permanent magnets having high corrosion resistance at low cost. When Co is too small, the corrosion resistance is lowered even if the Zr content is within the range described later. When Co is too much, the effect of improving corrosion resistance is peaked, and the cost also increases.
The Fe content is substantially the remainder of the R-T-B permanent magnet. The substantial remainder means the remainder excluding the above-mentioned R and Co, and B, Zr, M and other elements described later.
The content of B in the R-T-B-based permanent magnet according to the present embodiment is 0.90 mass% or more and 1.02 mass% or less, and may be 0.92 mass% or more and 1.00 mass% or less, based on 100 mass% of the total mass of the R-T-B-based permanent magnet. When B is too small, Hk/HcJ tends to decrease. When B is too much, HcJ becomes easy to decrease.
The R-T-B permanent magnet according to the present embodiment further contains Zr. The Zr content is 0.21-0.85 mass% based on 100 mass% of the total mass of the R-T-B permanent magnet. By containing Zr in the above range, abnormal growth of crystal grains at the time of sintering can be suppressed, and Hk/HcJ and magnetic susceptibility at low magnetic field can be improved. Further, even if the content of Co is within the above range, the corrosion resistance can be improved. When Zr is too small, abnormal grain growth during sintering becomes easy to occur, and the Hk/HcJ and the magnetic susceptibility under low magnetic field become poor. In addition, corrosion resistance is reduced. When Zr is excessive, Br and Hk/HcJ become liable to decrease.
The Zr/Co ratio may be 0.31 or more and 1.98 or less. The content may be 0.48 to 1.40, or 0.73 to 1.40. By controlling the Zr/Co ratio to be contained within the above range, an R-T-B permanent magnet having high corrosion resistance can be obtained even if expensive Co is reduced. As a result, it becomes easy to manufacture R-T-B permanent magnets having high corrosion resistance at low cost. When the Zr/Co ratio is too large, the corrosion resistance is lowered even if the Zr content is within the above range. When the Zr/Co ratio is too small, the effect of improving corrosion resistance is peaked, and the cost is also high. In particular, by setting the Zr/Co ratio to 0.48 or more and 1.40 or less, HcJ and Br tend to increase.
In general, the grain boundary phase of an R-T-B permanent magnet contains an R-rich phase having a higher mass concentration of R than the main phase. In the corrosion of the magnet by water vapor, hydrogen generated in the corrosion reaction is adsorbed by the R-rich phase present in the grain boundary of the magnet. Further, by allowing hydrogen to be adsorbed by the R-rich phase, R contained in the R-rich phase is easily changed to hydroxide. By changing R contained in the R-rich phase to hydroxide, the volume of the R-rich phase expands. Shedding of the main phase particles occurs by volume expansion of the R-rich phase. Further, it is considered that the erosion proceeds inside the magnet at an accelerated speed due to the falling-off of the main phase particles.
When the Zr content in the R-T-B permanent magnet is 0.21 mass% or more, the mass concentration of R in the R-rich phase is likely to decrease, and the mass concentration of Fe and the mass concentration of Zr are likely to increase, as compared with the case where the Zr content in the R-T-B permanent magnet is less than 0.21 mass%. When the R-T-B permanent magnet contains Cu, the mass concentration of Cu in the R-rich phase is also likely to increase. When the Zr content in the R-T-B permanent magnet is less than 0.21 mass%, the mass concentration of R in the R-rich phase is likely to be 65 mass% or more. On the other hand, when the Zr content is 0.21 mass% or more, the mass concentration of R in the R-rich phase tends to be low, and is likely to be 55 mass% or less, for example.
Further, in the case of an R-rich phase containing R at a low mass concentration and having high mass concentrations of the respective elements of Fe, Zr, and Cu, hydrogen is less likely to be adsorbed than in the case of an R-rich phase containing R at a mass concentration of 65 mass% or more and having low mass concentrations of the respective elements of Fe, Zr, and Cu. As a result, an R-T-B permanent magnet having high corrosion resistance even when the Co content is reduced can be obtained.
The content of Zr may be 0.25 mass% or more and 0.65 mass% or less, or may be 0.31 mass% or more and 0.60 mass% or less. In particular, by setting the Zr content to 0.25 mass% or more, the sintering stability temperature range is widened. That is, the effect of suppressing abnormal grain growth during sintering is further improved. Further, the degree of variation in characteristics is reduced, and the manufacturing stability is improved.
The R-T-B permanent magnet according to the present embodiment may further contain M. M is at least one selected from Cu, Mn, Al and Ga. The content of M is not particularly limited. M may not be contained. The total mass of the R-T-B permanent magnet is set to 100 mass%, and the mass may be 0 mass% or more and 1.3 mass% or less.
The content of Cu is not particularly limited. Cu may not be contained. The content of Cu may be 0.10 mass% or more and 0.55 mass% or less, may be 0.14 mass% or more and 0.53 mass% or less, or may be 0.20 mass% or more and 0.50 mass% or less, based on 100 mass% of the total mass of the R-T-B permanent magnet. When Cu is small, Br and HcJ are liable to decrease. Further, the corrosion resistance is also liable to decrease. When Cu is large, HcJ is easily decreased.
The content of Mn is not particularly limited. Mn may not be contained. The content of Mn may be 0.02 mass% or more and 0.10 mass% or less, may be 0.02 mass% or more and 0.06 mass% or less, or may be 0.02 mass% or more and 0.04 mass% or less, based on 100 mass% of the total mass of the R-T-B-based permanent magnet. When Mn is small, Br and HcJ are liable to decrease. When Mn is large, HcJ becomes easy to decrease.
The content of Al is not particularly limited. Al may not be contained. The content of Al may be 0.07 mass% or more and 0.35 mass% or less, may be 0.10 mass% or more and 0.30 mass% or less, or may be 0.15 mass% or more and 0.23 mass% or less, based on 100 mass% of the total mass of the R-T-B permanent magnet. When Al is small, HcJ becomes easy to decrease. Further, the change in magnetic properties (particularly HcJ) is large with respect to the change in aging temperature at the time of production or heat treatment temperature after grain boundary diffusion described later, and the production stability is liable to be lowered. When Al is large, Br is liable to decrease.
The content of Ga is not particularly limited. Ga may not be contained. The content of Ga may be 0.02 mass% or more and 0.15 mass% or less, or 0.04 mass% or more and 0.15 mass% or less, based on 100 mass% of the total mass of the R-T-B permanent magnet. When Ga is small, HcJ is liable to decrease. When Ga is large, a sub-phase such as R-T-Ga is likely to be contained in the grain boundary, and Br is likely to be reduced.
The R-T-B permanent magnet according to the present embodiment may contain, as another element, an element other than Nd, Pr, Dy, Tb, T, B, C, Zr, and M. The content of other elements is not particularly limited as long as it does not largely affect the magnetic properties and corrosion resistance of the R-T-B permanent magnet. For example, the total mass of the R-T-B permanent magnets is set to 100 mass%, and the total mass may be 1.0 mass% or less. Further, the content of rare earth elements other than Nd, Pr, Dy, and Tb may be 0.3 mass% or less in total.
Hereinafter, the contents of carbon (C), nitrogen (N), and oxygen (O) are described as examples of other elements.
The content of C in the R-T-B-based permanent magnet according to the present embodiment may be 0.15 mass% or less, 0.13 mass% or less, or 0.11 mass% or less, based on 100 mass% of the total mass of the R-T-B-based permanent magnet. The content of C may be 0.06 mass% or more and 0.15 mass% or less, 0.06 mass% or more and 0.13 mass% or less, or 0.06 mass% or more and 0.11 mass% or less. By setting the C content to 0.15 mass% or less, HcJ tends to be improved. In particular, the content of C may be 0.11 mass% or less from the viewpoint of improving HcJ. In addition, the load on the process is large when manufacturing an R-T-B permanent magnet in which the C content is less than 0.06 mass%. Therefore, it is difficult to produce an R-T-B permanent magnet having a C content of less than 0.06 mass% at low cost. In addition, the content of C may be 0.10 mass% or more and 0.15 mass% or less, particularly from the viewpoint of improving Hk/HcJ.
The content of N in the R-T-B-based permanent magnet according to the present embodiment may be 0.12 mass% or less, 0.11 mass% or less, or 0.105 mass% or less, based on 100 mass% of the total mass of the R-T-B-based permanent magnet. The content may be 0.025% by mass or more and 0.12% by mass or less, 0.025% by mass or more and 0.11% by mass or less, or 0.025% by mass or more and 0.105% by mass or less. The smaller the content of N, the easier the HcJ content becomes to increase. In addition, the load on the process is large when manufacturing an R-T-B permanent magnet having an N content of less than 0.025 mass%. Therefore, it is difficult to produce an R-T-B permanent magnet having an N content of less than 0.025 mass% at low cost.
The content of O in the R-T-B-based permanent magnet according to the present embodiment may be 0.10 mass% or less, 0.08 mass% or less, 0.07 mass% or less, or 0.05 mass% or less, based on 100 mass% of the total mass of the R-T-B-based permanent magnet. Further, the content may be 0.035 to 0.05 mass%. In addition, the load on the process is large for manufacturing an R-T-B permanent magnet having an O content of less than 0.035 mass%. Therefore, it is difficult to produce an R-T-B permanent magnet having an O content of less than 0.035 mass% at low cost.
As the method for measuring various components contained in the R-T-B-based permanent magnet according to the present embodiment, conventionally generally known methods can be used. The amounts of the respective elements can be measured by, for example, fluorescent X-ray analysis, inductively coupled plasma emission spectrometry (ICP analysis), and the like. The content of O can be measured, for example, by an inert gas melting-non-dispersive infrared absorption method. The C content can be determined, for example, by combustion-infrared absorption in an oxygen stream. The content of N can be measured, for example, by an inert gas melt-thermal conductivity method.
The shape of the R-T-B permanent magnet according to the present embodiment is not particularly limited. For example, the shape may be a rectangular parallelepiped.
Hereinafter, the method for manufacturing the R-T-B-based permanent magnet will be described in detail, but the method for manufacturing the R-T-B-based permanent magnet is not limited thereto, and other known methods may be used.
[ preparation Process of raw Material powder ]
The raw material powder can be produced by a known method. In the present embodiment, a case of the 1-alloy method using a single alloy is described, but a so-called 2-alloy method in which 2 or more kinds of alloys having different compositions are mixed to prepare a raw material powder may be used.
First, a raw material alloy for an R-T-B permanent magnet is prepared (alloy preparation step). In the alloy preparation step, a raw material metal corresponding to the composition of the R-T-B permanent magnet according to the present embodiment is melted by a known method, and then a raw material alloy having a desired composition is produced by casting.
As the raw material metal, for example, a single rare earth element, a single metal element such as Fe, Co, Cu, or the like, an alloy composed of a plurality of metals (for example, Fe — Co alloy), a compound composed of a plurality of elements (for example, ferroboron) or the like can be suitably used. The casting method for casting the raw material alloy from the raw material metal is not particularly limited. A strip casting method is used to obtain an R-T-B permanent magnet having high magnetic properties. The obtained raw material alloy may be homogenized by a known method as needed.
The raw material alloy is produced and then pulverized (pulverization step). The atmosphere in each of the pulverizing step to the sintering step may be a low oxygen concentration from the viewpoint of obtaining high magnetic properties. For example, the oxygen concentration in the atmosphere in each step may be 200ppm or less. The O content in the R-T-B permanent magnet can be controlled by controlling the oxygen concentration in the atmosphere in each step.
Hereinafter, as the above-mentioned pulverizing step, a case will be described below in which the pulverizing step is performed in 2 stages of a coarse pulverizing step of pulverizing to a particle size of several hundred μm to several mm and a fine pulverizing step of performing fine pulverizing to a particle size of several μm, but the pulverizing step may be performed in only 1 stage of the fine pulverizing step.
In the coarse pulverization step, coarse pulverization is carried out until the particle size becomes about several hundred μm to several mm. Thus, a coarsely pulverized powder was obtained. The method of the coarse pulverization is not particularly limited, and the pulverization can be carried out by a known method such as a method of hydrogen adsorption pulverization or a method using a coarse pulverizer. In the case of hydrogen adsorption pulverization, the N content in the R-T-B permanent magnet can be controlled by controlling the nitrogen concentration in the atmosphere at the time of dehydrogenation treatment.
Next, the obtained coarsely pulverized powder is finely pulverized until the average particle size becomes several μm (finely pulverizing step). Thus, a finely pulverized powder (raw material powder) was obtained. The average particle diameter of the fine powder may be 1 to 10 μm, 2 to 6 μm, or 2 to 4 μm. The N content in the R-T-B permanent magnet can be controlled by controlling the nitrogen concentration in the atmosphere in the fine grinding step.
The method of the fine pulverization is not particularly limited. For example, it can be carried out by a method using various micro-crushers.
When the above-mentioned coarsely pulverized powder is finely pulverized, various pulverizing aids such as lauric acid amide and oleic acid amide can be added to obtain a finely pulverized powder in which crystal grains are easily oriented in a specific direction when molded by pressing in a magnetic field. The content of C in the R-T-B permanent magnet can be controlled by changing the amount of the grinding aid added.
[ Molding Process ]
In the molding step, the finely pulverized powder is molded into a desired shape. The molding method is not particularly limited. In the present embodiment, the finely pulverized powder is filled in a mold and pressurized in a magnetic field. Since the crystal grains of the molded article thus obtained are oriented in a specific direction, an R-T-B permanent magnet having a higher Br can be obtained.
The pressing during molding may be performed at 20MPa or more and 300MPa or less. The applied magnetic field may be 950kA/m or more, or 950kA/m or more and 1600kA/m or less. The applied magnetic field is not limited to the static magnetic field, and may be a pulse-like magnetic field. In addition, a static magnetic field and a pulse-like magnetic field may be used in combination.
As the molding method, in addition to the dry molding in which the fine powder is directly molded as described above, wet molding in which slurry obtained by dispersing the fine powder in a solvent such as oil is molded can be applied.
The shape of the molded article obtained by molding the finely pulverized powder is not particularly limited. The density of the molded article at this time point may be 4.0Mg/m3～4.3Mg/m3。
[ sintering Process ]
The sintering step is a step of sintering the molded body in a vacuum or an inert gas atmosphere to obtain a sintered body. The sintering conditions need to be adjusted according to various conditions such as composition, pulverization method, difference in particle size and particle size distribution. For example, the molded article is formed by, for example, conducting the reaction at 1000 ℃ or higher and 1200 ℃ or lower in vacuum or in an inert gas atmosphere for 1 hour or longer and 2 hours or longerSintering is carried out by heating treatment for 0 hour or less. By sintering under the above-mentioned sintering conditions, a sintered body having a high density can be obtained. In this embodiment, at least 7.45Mg/m is obtained3A sintered body having the above density. The density of the sintered body may be 7.50Mg/m3The above.
[ aging treatment Process ]
The aging treatment step is a step of heat-treating (aging treatment) the sintered body at a temperature lower than the sintering temperature. Whether or not the aging treatment is performed is not particularly limited, and the number of times of the aging treatment is also not particularly limited, and the aging treatment may be appropriately performed according to desired magnetic characteristics. The grain boundary diffusion step described later may also serve as the aging treatment step. Hereinafter, an embodiment in which 2 times of aging treatment is performed will be described.
The first aging step is a first aging step, the second aging step is a second aging step, the aging temperature in the first aging step is T1, and the aging temperature in the second aging step is T2.
T1 and the aging time in the first aging step are not particularly limited. T1 may be set to 700 ℃ or higher and 900 ℃ or lower. The aging time may be 1 hour or more and 10 hours or less.
T2 and the aging time in the second aging step are not particularly limited. T2 may be 450 ℃ or higher and 700 ℃ or lower. The aging time may be 1 hour or more and 10 hours or less.
The magnetic properties, particularly HcJ, of the finally obtained R-T-B permanent magnet can be improved by the aging treatment.
[ working Process (before grain boundary diffusion) ]
The sintered body according to the present embodiment may be processed into a predetermined shape as needed. Examples of the processing method include shape processing such as cutting and grinding, and chamfering such as barrel polishing.
[ procedure of grain boundary diffusion ]
The grain boundary diffusion step may be performed by adhering a diffusion material to the surface of the sintered body and heating the sintered body to which the diffusion material is adhered. Thus, an R-T-B permanent magnet was obtained. In the present embodiment, the kind of the diffusion material is not particularly limited. The diffusion material may contain a heavy rare earth element (e.g., Tb and/or Dy), and the diffusion material may contain all of the following first to third components. The first component is a hydride of Tb and/or a hydride of Dy. The second component is a hydride of Nd and/or a hydride of Pr. The third component is a Cu-containing monomer, a Cu-containing alloy, and/or a Cu-containing compound.
In the diffusion step, as the temperature rises, the grain boundary phase at which the concentration of the rare earth element R is high in the grain boundary of the magnet base material (sintered body) is transformed into a liquid phase, and the diffusion material is dissolved into the liquid phase, whereby the component of the diffusion material diffuses from the surface of the magnet base material into the interior of the magnet base material. When a hydride of a heavy rare earth element RH is used as a diffusion material, the RH hydride adhering to the surface of the magnet base material is likely to be rapidly dissolved in a liquid phase exuded from the magnet base material to the surface when a dehydrogenation reaction occurs due to a temperature rise. As a result, the concentration of RH rapidly increases near the surface of the magnet base material, and diffusion of RH into the main phase particles located near the surface of the magnet base material is likely to occur. As a result, RH is likely to stay in the main phase particles located near the surface of the magnet base material, and is less likely to diffuse into the magnet base material. Therefore, RH diffused in the magnet is reduced, and the increase in coercive force of the permanent magnet is reduced.
In the case where the diffusion material contains the first component (heavy rare earth element RH), the second component (light rare earth element RL) and the third component (Cu), when the liquid phase having a high concentration of R generated in the magnet base material bleeds out to the vicinity of the diffusion material on the surface, the eutectic temperature of Cu and R is low, so that Cu contained in the diffusion material is easily dissolved in advance of the liquid phase. Therefore, first, dissolution of Cu into the liquid phase occurs, and the Cu concentration in the liquid phase in the vicinity of the surface of the magnet base material increases. As a result, an R — Cu-rich liquid phase is generated near the surface of the magnet base material, and Cu further diffuses into the liquid phase inside the magnet base material. After the hydride dehydrogenation reaction occurs, RL as the second component and RH as the first component are dissolved into the R — Cu-rich liquid phase. The eutectic temperature of RL and Cu as the second component is about 500 ℃, and the eutectic temperature of RH and Cu as the first component is about 700-800 ℃. Therefore, RL as the second component after Cu dissolves in the R — Cu-rich liquid phase near the surface of the magnet base material, and then RH as the first component dissolves. By the dissolution of RL as the second component subsequent to Cu, diffusion of Cu into the interior of the magnet is promoted, and an R — Cu-rich liquid phase is generated in the grain boundary of the magnet base material.
The first component (RH) of the first component (RH), the second component (RL) and the third component (Cu) is likely to be finally dissolved in the liquid phase. Therefore, since RH derived from the first component diffuses into the liquid phase inside the magnet base material after Cu and RL, a rapid increase in RH concentration in the vicinity of the surface of the magnet base material can be suppressed as compared with the case where Cu and RL are not present. Therefore, diffusion of RH into the main phase particles located in the vicinity of the surface of the magnet base material can be suppressed. As a result, the RH diffused in the magnet increases, and the coercive force of the permanent magnet is easily improved.
The diffusion material may be a slurry containing a solvent in addition to the first to third components. The solvent contained in the slurry may be a solvent other than water. For example, an organic solvent such as alcohol, aldehyde, ketone, etc. may be used. In addition, the diffusion material may contain a binder. The kind of the binder is not particularly limited. For example, a resin such as an acrylic resin may be contained as the binder. By containing the binder, the diffusion material is easily attached to the surface of the sintered body.
The diffusion material may be a paste containing a solvent and a binder in addition to the above-described first to third components. The paste has fluidity and high viscosity. The viscosity of the paste is higher than that of the paste.
The sintered body to which the slurry or paste is attached may be dried and the solvent may be removed before the grain boundary diffusion.
The diffusion treatment temperature in the grain boundary diffusion step according to the present embodiment may be equal to or higher than the eutectic temperature of RL and Cu, or may be lower than the sintering temperature. For example, the diffusion treatment temperature may be 800 ℃ or higher and 950 ℃ or lower. In the grain boundary diffusion step, the temperature of the magnet base material may be gradually increased from a temperature lower than the diffusion treatment temperature to the diffusion treatment temperature.
The time for maintaining the temperature of the base material at the diffusion treatment temperature (diffusion treatment time) may be, for example, 1 hour or more and 50 hours or less. The atmosphere around the substrate in the diffusion treatment process may be a non-oxidizing atmosphere. The non-oxidizing atmosphere may be a rare gas such as argon. The pressure of the atmosphere around the magnet base material in the diffusion step may be 1kPa or less. By setting the reduced-pressure atmosphere as described above, the dehydrogenation reaction of the hydride is promoted, and the diffusion material is easily dissolved into the liquid phase.
Further, after the diffusion treatment, a heat treatment may be further performed. The heat treatment temperature in that case may be 450 ℃ or more and 600 ℃ or less. The heat treatment time may be 1 hour or more and 10 hours or less. By performing such heat treatment, the magnetic properties, particularly HcJ, of the R-T-B permanent magnet to be finally obtained can be improved.
The manufacturing stability of the R-T-B permanent magnet according to the present embodiment can be determined by, for example, the magnitude of the amount of change in magnetic properties with respect to the change in the diffusion treatment temperature in the grain boundary diffusion step and/or the heat treatment temperature after diffusion of the heavy rare earth element.
[ working Process (after grain boundary diffusion) ]
After the grain boundary diffusion step, polishing may be performed to remove the diffusion material remaining on the surface of the R-T-B-based permanent magnet. Further, the R-T-B permanent magnet may be subjected to other processing. For example, the surface may be processed by shaping such as cutting or grinding, or chamfering such as barrel polishing.
In the present embodiment, the processing steps before and after grain boundary diffusion are performed, but these steps are not necessarily performed. The grain boundary diffusion step may also serve as an aging step. The heating temperature in the case where the grain boundary diffusion step also serves as the aging step is not particularly limited. The temperature preferable in the grain boundary diffusion step is preferable, and the temperature preferable in the aging step is particularly preferable.
In particular, the R-T-B permanent magnet after grain boundary diffusion tends to have a concentration distribution in which the concentration of the heavy rare earth element decreases from the outer side toward the inner side of the R-T-B permanent magnet. In addition, the main phase particles contained in the R-T-B permanent magnet after grain boundary diffusion easily have the above-described core-shell structure.
The R-T-B permanent magnet according to the present embodiment thus obtained has desired characteristics. Specifically, Br, HcJ, and Hk/HcJ are high, and corrosion resistance and manufacturing stability are also excellent. Further, the temperature characteristics were also good, HcJ at high temperature was high, and decrease of HcJ with respect to temperature increase was small.
The R-T-B permanent magnet according to the present embodiment obtained by the above-described method becomes a magnetized R-T-B permanent magnet by magnetization.
The R-T-B permanent magnet according to the present embodiment is suitably used for a motor, a generator, and the like.
The present invention is not limited to the above-described embodiments, and various changes can be made within the scope of the present invention.
The method of manufacturing the R-T-B permanent magnet is not limited to the above-described method, and may be appropriately modified. For example, the above-mentioned method for producing an R-T-B-based permanent magnet is a sintering method, and the R-T-B-based permanent magnet according to the present embodiment may be produced by hot working. A method for producing an R-T-B permanent magnet by hot working includes the following steps.
(a) Melting raw material metal, and quenching the obtained molten metal to obtain a thin strip;
(b) a pulverization step of pulverizing the thin strip to obtain a flake-like raw material powder;
(c) a cold forming step of cold forming the pulverized raw material powder;
(d) a preheating step of preheating the cold-formed body;
(e) a thermoforming step of thermoforming the preheated cold-formed body;
(f) a thermoplastic processing step of plastically deforming the thermoformed body into a predetermined shape;
(g) and an aging treatment step of aging the R-T-B permanent magnet.
The steps after the aging treatment step are similar to those in the case of production by sintering.
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